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APPLICATION NOTE
Insertion Loss
Measurement Methods
SITE MASTERTM
Introduction
Transmission feed line system performance plays an important
Antenna
role in wireless network coverage. Insertion loss measurement
is one of the critical measurements used to analyze transmission Antenna
Jumper Main Feeder Jumper
feed line installation and performance quality. This application
note explains how Site Master is used to measure cable insertion
loss with different test methods and how to predict the maxi- Connectors
mum allowable cable insertion loss through manual calculations.
In wireless communication systems, the transmit and receive Figure 1. Typical transmission line system
antennas are connected to the radio through coaxial cable
and/or waveguide transmission lines (Figure 1).
Insertion loss measures the energy absorbed by the transmission Measurement Methods
line in the direction of the signal path in dB/meter or dB/feet. During network deployment, mainte-
Transmission line losses are dependent on cable type, operating nance, and trouble shooting phases,
frequency and the length of the cable run. Insertion loss of a insertion loss can be measured by dis-
cable varies with frequency; the higher the frequency, the connecting the antenna and connecting
greater the loss. an enclosed short at the end of the
Insertion loss measurements help troubleshoot the network transmission line. If a Tower Mounted
by verifying the cable installation and cable performance. Amplifier (TMA) is used in the transmis-
High insertion loss in the feedline or jumpers can contribute sion feed line system, it is best to remove
to poor system performance and loss of coverage. Measuring the TMA and antenna from the system
insertion loss using Site Master assures accurate and repeatable configuration to perform an insertion
measurements. loss measurement. It is best to always dis-
connect the cable at the same location
so the measured data can be compared
to the historical data for accuracy and
repeatability.
Using Site Master, cable insertion loss
can be measured in CABLE LOSS or
RETURN LOSS mode. In Cable Loss
mode, Site Master automatically consid-
ers the signal traveling in both directions
thus making the measurement easier for
the user in the field.
The following section explains the pro-
cedure to measure insertion loss in cable
loss mode and return loss mode. The
measurement setup and equipment
required is the same for both modes.
Verify Cable Insertion Loss
From Ground Level
Application Note
Step 4. Connect the phase stable test
Measuring Insertion Loss Measurement port extension cable to the
Insertion Loss Setup RF port.
The insertion loss measurement set up Step 5. Calibrate the Site Master at the
Using CABLE for a typical transmission feed line end of the phase stable test port
LOSS MODE system is shown in Figure 2. Remove extension cable. (See the
the antenna and connect an enclosed section entitled "Calibrating
precision "short" at the end of the Site Master with the Phase
Required Equipment transmission line. Stable Test Port Extension
If a Tower Mounted Amplifier (TMA) Cable" for details.)